1. Field of the Invention
The present invention relates to an optical element which has a diffraction grating and a plurality of mirror surfaces and is molded by plastic molding, its manufacturing method and an optical element manufacturing metal die suited for use to manufacture the optical element.
2. Description of the Prior Art
Up to now, various kinds of patterning methods utilizing a lithography have been known and optical elements such as an optical integrated device, a diffraction grating and the like which are manufactured based on the patterning methods have become commercialized.
These optical elements are generally manufactured as follows. First of all, a resist is coated on a surface of glass and a pattern is drawn on the resist to make a resist pattern. Next, using the resist pattern as a master, a nickel master (stamper) is obtained by way of a nickel electroforming method.
Then, using the nickel master, the optical elements can be obtained by a method of, for example, pressing a film against the master or by a method (a so-called 2 P method) of, for example, pouring ultraviolet-setting resin on the master and then hardening it by way of ultraviolet irradiation to peel off a replica.
Also, in some cases, there are injection molded products, as represented by a general optical disc such as a compact disc and the like, on one surface or both surfaces of which a pattern or patterns are formed. Such products can be obtained by carrying out injection molding of resin after setting the above-mentioned master to an injection molding machine.
However, with the above-mentioned respective manufacturing methods, the surface on which a pattern is formed is limited to a plane. This makes it difficult to manufacture those complex structures of, for example, a structure having an inclined surface which is angled relative to a main surface in a plane where a pattern exists such as Foucault prism and a structure having a level difference in a plane where a pattern exists.
Further, when an optical element having mirror surfaces is formed by way of an injection molding method and the like, it is necessary to obtain predetermined flatness as well as roughness of a surface of a mirror forming portion in a metal die for forming a mirror surface of the optical element by polish-working (i.e., polishing), for example, after carrying out grind-working thereon using a grind stone.
For this reason, in a case of manufacturing a shape wherein a horizontal surface and an inclined surface mixedly exist as in, for example, the above-mentioned Foucault prism, it is necessary to divide a nesting in a metal die being a portion forming the shape into a plurality of nestings such as one for forming the horizontal surface and another for forming the inclined surface. Consequently, there is an increase in the number of parts of the metal die, which makes not only assembling of the metal die complicated but also the overall precision of the metal die inaccurate due to accumulation of mechanical shape precision of each of the nestings. Therefore, it becomes impossible to obtain a micron-order dimensional precision necessary for the optical element as a molded product.
Moreover, particularly in the case of the Foucault prism, when the nesting of the metal die is divided into a plurality of nestings to form the optical element, molding flashes occur at a joint plane of respective nestings. The optical element wherein flashes occur at the joint plane has involved a problem that optical characteristics deteriorate when a laser beam passes through the joint plane between the horizontal surface and the inclined surface.
In order to solve the above-mentioned problems, the present invention provides an optical element which has a complex structure such as the diffraction grating, the inclined surface, the difference in level, a curved surface and the like as well as has good optical characteristics, its manufacturing method and an optical element manufacturing metal die capable of injection molding even the optical element having a complex structure.
An optical element of the present invention has a plurality of mirror surfaces including at least two adjoining mirror surfaces and is formed by plastic molding with a metal die, the metal die being constituted to have at least one or more nestings each of which has a mirror surface forming portion, and the two adjoining mirror surfaces being molded by two adjoining mirror surface forming portions formed on the same nesting.
According to the optical element of the present invention, because it is molded by the two adjoining mirror surfaces forming portions integrated into the same nesting, there occurs no molding flashes at the joint plane between the two mirror surfaces as well as no deterioration of optical characteristics at the joint plane.
A manufacturing method of the optical element of the present invention is such that the metal die for carrying out the plastic molding has at least one or more nestings each of which has a plurality of adjoining mirror forming portions and the plurality of adjoining mirror surfaces of the optical element are molded by a plurality of mirror surface forming portions of the same nesting.
According to the manufacturing method of the optical element of the present invention, by molding the plurality of adjoining mirror surfaces of the optical element by the plurality of adjoining mirror surface forming portions, the optical element can be manufactured without generating molding flashes at the joint plane of a plurality of mirror surfaces.
The manufacturing method of the optical element of the present invention is such that the metal die for carrying out the plastic molding has at least one or more nestings each of which has a plurality of the mirror surface forming portions, at least one or more mirror surface forming portions of the plurality of mirror surface forming portions of the nesting being formed by a mirror surface grinding method, and a mirror surface of the optical element being molded by the mirror surface forming portion.
According to the above-mentioned manufacturing method of the optical element of the present invention, by forming at least one or more mirror surface forming portions by the mirror surface grinding method, one of two mirror surfaces having two mirror surfaces which form an angle, for example, between a horizontal surface and an inclined surface or one of two mirror surfaces having a difference in level can be molded using the mirror surface forming portion formed by the mirror surface grinding method. This makes it possible to manufacture the optical element having a complex structure such as the inclined surface, the difference in level and the like.
The optical element manufacturing metal die of the present invention is constituted to have at least one or more nestings each of which comprises the plurality of adjoining mirror surface forming portions for molding the mirror surfaces of the optical element.
According to the above-mentioned optical element manufacturing metal die of the present invention, because the nesting has the plurality of adjoining mirror surface forming portions, it is possible to carry out the molding without generating the molding flashes at the joint plane between the mirror surfaces of the optical element which are molded by the plurality of mirror surface forming portions.
The optical element manufacturing metal die of the present invention is constituted to have at least one or more nestings each of which has the plurality of mirror surface forming portions for molding the mirror surfaces of the optical element and at least one or more mirror surface forming portions of the plurality of mirror surface forming portions of the nesting are formed by the mirror surface grinding method.
According to the optical element manufacturing metal die of the present invention, because at least one or more mirror surface forming portions are formed by the mirror grinding method out of the plurality of mirror surface forming portions of the nesting, one of the two mirror surfaces making an angle, for example, between the horizontal surface and the inclined surface or one of the two mirror surfaces having a difference in level can be molded by the mirror ground portion formed by the mirror surface grinding method. This makes it possible to manufacture the optical element of a structure having the two mirror surfaces forming an angle, the two mirror surfaces having a difference in level and the like.
The optical element manufacturing metal die of the present invention is constituted to include a nesting having a diffraction grating forming portion in which a concavo-convex pattern for molding the diffraction grating of the optical element is formed on at least one surface of a substrate.
According to the above-mentioned optical element manufacturing metal die of the present invention, because it has the diffraction grating forming portion wherein the predetermined concavo-convex pattern is formed on at least one surface of the substrate of the nesting in the metal die, it is possible to carry out the molding of the optical element having the diffraction grating more easily than the conventional molding method using a nickel master.